Encapsulated iron-based oxygen reduction electrocatalysts by high pressure pyrolysis

Abstract

Non-precious metal catalysts (NPMCs) are candidate materials to replace platinum for proton exchange membrane fuel cells (PEMFCs). Herein we reported a type of iron-based NPMCs prepared by high pressure pyrolysis for the oxygen reduction reaction (ORR) in acidic media. The catalysts are in form of carbon microspheres in a sub-microscale consisting of iron-containing nanoparticles encapsulated by graphitic layers. By tailoring temperatures and duration of pyrolysis, the best ORR catalyst was achieved at 700 °C and 75 min, which exhibits an onset potential of 0.85 V at 0.1 mA cm−2 and a half-wave potential of 0.72 V in acid media. After 10,000 potential cycles, only 25 mV shift of half-wave potential is observed showing excellent stability. An analogue material prepared from nitrogen-free precursors shows significant electrochemical activity though it is much lower than that from the nitrogen containing precursors and can be improved by post treatment in ammonia. These results indicate the contribution to the catalysis from surface nitrogen functionalities and encapsulated metal-containing nanoparticles.